We will examine the hypothesis that exposure to inhibitors of protein synthesis immediately before and during hyperthermia protects cells against the lethal effects of heat by protecting against post-hyperthermia inhibition of protein synthesis. We will then determine if the cycloheximide treatment protects cells against chromosome aberrations induced by heat during the S phase that are responsible for cell killing. Next we will measure the effects of cycloheximide before and during hyperthermia on protection against hyperthermia-induced radiosensitization during the S phase. One aspect of the hypothesis that thermotolerance is due to the synthesis of recovery proteins will be tested. This will be done by examining the effects of a further temperature shock on maximally thermotolerant cells with cycloheximide present before and during the second exposure to hyperthermia.